1. Field of the Art
This invention relates to a normally closed or normally open auto-drainage assembly (hereinafter referred to simply as "auto-drain" for brevity) to be inserted into a pneumatic piping system, which supplies pressurized air to a pneumatically operating machine, for the purpose of separating and discharging a drain liquid from the pneumatic piping.
2. Description of the Prior Art
Auto-drains have been known and in use for automatically discharging a drain liquid, including two types of auto-drains: a normally closed auto-drain which is arranged to hold a drain valve body normally in a closed position in relation with a downward movement of a float to stop drain discharges when a drain reservoir case is internally in a pressurized state under the influence of a prevailing fluid pressure and when the drain liquid level is at a low position, opening the drain valve body and discharging the drain liquid out of the reservoir case as soon as the drain liquid level rises to push up the float; and a normally open auto-drain which is arranged to hold a drain valve body normally in an open position to discharge a drain liquid when a drain reservoir case is in a non-pressurized state, closing a drain discharge passage with the drain valve body to stop drain discharging when the reservoir case is internally pressurized similarly unless the float is pushed up by elevation of the drain liquid level.
Illustrated by way of example in FIG. 15 is a conventional normally closed auto-drain 1 including: a drain reservoir case 2 for storing a drain liquid which flows in from above along with pressurized air; a drain discharge guide sleeve 3 which is fitted in an opening at the bottom of the case 2; a drain valve seat 4 which is formed on the inner periphery of a hollow discharge guide shaft 3; a manual valve support member 5 which is fixed on a lower portion of the discharge guide shaft 3; and a manual operating member 6. Below the drain valve seat 4, the discharge guide shaft 3 is formed in a larger diameter than the drain valve seat 4 to provide a drain discharging passage.
A float guide 8 which is connected to an upper portion of the discharge guide shaft 3 is provided with a cylindrical guide portion to guide upward and downward movements of a float 9. A hollow cylindrical piston 10 is slidably fitted in the float guide 8, the piston 10 having a drain valve body (a seal member) 11 fitted on the circumference of its lower hollow shaft portion to close and open a drain passage by seating and unseating the drain valve body on and off the drain valve seat 4.
Defined by the piston 10 within the float guide 8 are an upper pilot chamber 12 and a lower pressure chamber 13 which is communicated with the reservoir case 2 through radial intercommunicating slots 8a. A pilot valve seat 14 opening into the pilot chamber 12 is formed at the upper end of the cylindrical guide portion of the float guide. The pilot valve seat 14 is opened and closed by a pilot valve body 15 which is mounted on a lever 17, which is in turn rockably supported at one end thereof on the upper end of the float guide 8 and linked at the other end to the float 9 through a holder member 18. The piston 10 is internally provided with a partition wall which is formed with an orifice 19 of a smaller diameter than the above-described pilot valve seat 14, thereby communicating the pilot chamber 12 with the inner cavity of the hollow cylindrical piston 10 which is opened to the outside through the manual operating member 6. Further, a first spring 21 is charged in the pilot chamber 12 to bias the piston 10 in the downward direction, while a second spring 22 is charged between the piston 10 and a lifting tube 6a of the manual operating member 6 to bias the piston 10 in the upward direction.
With the known auto-drain of the above-described construction, the float 9 is lowered to close the pilot valve seat 14 with the pilot valve body 15 when the reservoir case is internally pressurized by influent pressurized air and the drain liquid level is at a low position as shown in the drawing, communicating the pilot chamber 12 with the outside through the orifice 19 and holding the piston 10 in a neutral position under the influence of the opposingly acting forces of the springs 21 and 22, and thus closing the drain valve body 11 on the drain valve seat 4.
As the float 9 is pushed up by a rising drain liquid level, the lever 17 is turned counterclockwise in the drawing, and therefore the pilot valve body 15 is unseated to open the pilot valve seat 14, permitting pressurized air in the case 2 to flow into the pilot chamber 12. As a result, the piston 10 is moved in the downward direction, unseating the drain valve body 11 to open the drain valve seat 4, discharging the drain liquid in the case 2 to the outside through the radial intercommunicating slots 8a and the lifting tube 6a of the manual operating member 6 via the circumference of the drain valve body 11.
When the float 9 is lowered by a drop of the drain liquid level, the pilot valve body 15 is seated to close the pilot valve seat 14, and the air pressure in the pilot chamber 12 is gradually reduced by air bleeding through the orifice 19. Consequently, the piston 10 is gradually returned to the neutral position, seating the drain valve body 11 in closed state on the drain valve seat 4 after a lapse of a short time period to stop the drain discharging.
In case of the known auto-drain as described above, due to the existence of a clearance between the drain valve body 11 on the outer periphery of the piston 10 and the inner periphery of the discharge guide shaft 3, the downward movements of the piston 10 toward the drain discharging position involve problems such as inclinations of the piston 10 during its downward movements or dislocation of the drain valve body or seal member 11 from its position on the drain valve body 11 under the influence of gushing streams of the drain liquid being discharged. Therefore, the piston 10 sometimes fails to return to the initial position or the drain valve seat 4 is left open after finishing a drain discharging operation.
Although the problems or drawbacks of conventional auto-drains have been explained above in connection with a normally closed type auto-drain, the same applies to normally open type auto-drains which are arranged to hold the drain valve normally in an unseated open position off the drain valve seat when no pressure prevails in the reservoir case 2.
Further, despite the similarities in function between the normally closed and normally open auto-drains, it has been the usual practice to build these two types of auto-drains by completely separate fabrication processes due to difficulties of using common component parts for the two types of auto-drains. In this regard, from the standpoint of reducing the production cost and facilitating the management of component parts, it is desirable to develop a universal auto-drain construction which can be arranged into either a normally closed type or a normally open type basically by the use of common component parts.